P. Kailuweit

Coulomb-Interaction-Induced Incomplete Shell Filling in the Hole System of InAs Quantum Dots

We have studied the hole charging spectra of self-assembled InAs quantum dots in perpendicular magnetic fields by capacitance-voltage spectroscopy. From the magnetic-field dependence of the individual peaks we conclude that the s-like ground state is completely filled with two holes but that the fourfold degenerate p shell is only half filled with two holes before the filling of the d shell starts. The resulting six-hole ground state is highly polarized. This incomplete shell filling can be explained by the large influence of the Coulomb interaction in this system.

Fabrication of genuine single-quantum-dot light-emitting diodes

We present a simple approach for the fabrication of genuine single quantum-dot light-emitting diodes. A submicron wide bottom contact stripe is formed by focused ion beam implantation doping into a GaAs buffer layer. Successive overgrowth with a thin intrinsic layer incorporating self-assembled InAs quantum dots, followed by a top contact layer of complementary doping type and standard photolithographic processing, allows for electrical cross sections in the sub-μm2 range. In devices with sufficiently low dot densities, only one single dot is expected to be electrically addressed. Both the observed current versus voltage characteristics and the evolution of the electroluminescence spectra as a function of applied voltage clearly demonstrate that this goal has been achieved.

Experimental imaging and atomistic modeling of electron and hole quasiparticle wave functions in InAs/GaAs quantum dots

We present experimental magnetotunneling results and atomistic pseudopotential calculations of quasiparticle electron and hole wave functions of self-assembled InAs/GaAs quantum dots. The combination of a predictive theory along with the experimental results allows us to gain direct insight into the quantum states. We monitor the effects of (i) correlations, (ii) atomistic symmetry, and (iii) piezoelectricity on the confined carriers and (iv) observe a peculiar charging sequence of holes that violates the Aufbau principle.

Si accumulation at the surface upon re-evaporation of Si-doped GaAs(100)

We have studied the in situ re-evaporation of Si-doped GaAs(100) and subsequent overgrowth with GaAs. Using capacitance–voltage spectroscopy, we found an accumulation of free carriers at the interface between the original GaAs and the regrown material. This shows that Si from the re-evaporated layer is not desorbed but is accumulated in a region near to the surface. We propose an exchange between Si atoms on the surface with Ga atoms in the first layer during the re-evaporation process as the underlying atomistic mechanism. The upper limit for the lateral diffusion length during the re-evaporation process was estimated to be 1 μm from re-evaporation experiments employing lateral resolved doping by focused ion beam implantation.